// Formatting library for C++ - chrono support
//
// Copyright (c) 2012 - present, Victor Zverovich
// All rights reserved.
//
// For the license information refer to format.h.

#ifndef ABEL_STRINGS_INTERNAL_CHRONO_H_
#define ABEL_STRINGS_INTERNAL_CHRONO_H_

#include <chrono>
#include <ctime>
#include <locale>
#include <sstream>

#include "abel/strings/internal/format.h"
#include "abel/strings/internal/locale.h"

FMT_BEGIN_NAMESPACE

// Enable safe chrono durations, unless explicitly disabled.
#ifndef FMT_SAFE_DURATION_CAST
#  define FMT_SAFE_DURATION_CAST 1
#endif
#if FMT_SAFE_DURATION_CAST

// For conversion between std::chrono::durations without undefined
// behaviour or erroneous results.
// This is a stripped down version of duration_cast, for inclusion in fmt.
// See https://github.com/pauldreik/safe_duration_cast
//
// Copyright Paul Dreik 2019
namespace safe_duration_cast {

template<typename To, typename From,
        FMT_ENABLE_IF(!std::is_same<From, To>::value &&
                      std::numeric_limits<From>::is_signed ==
                      std::numeric_limits<To>::is_signed)>
constexpr To lossless_integral_conversion(const From from, int &ec) {
    ec = 0;
    using F = std::numeric_limits<From>;
    using T = std::numeric_limits<To>;
    static_assert(F::is_integer, "From must be integral");
    static_assert(T::is_integer, "To must be integral");

    // A and B are both signed, or both unsigned.
    if (F::digits <= T::digits) {
        // From fits in To without any problem.
    } else {
        // From does not always fit in To, resort to a dynamic check.
        if (from < (T::min)() || from > (T::max)()) {
            // outside range.
            ec = 1;
            return {};
        }
    }
    return static_cast<To>(from);
}

/**
 * converts From to To, without loss. If the dynamic value of from
 * can't be converted to To without loss, ec is set.
 */
template<typename To, typename From,
        FMT_ENABLE_IF(!std::is_same<From, To>::value &&
                      std::numeric_limits<From>::is_signed !=
                      std::numeric_limits<To>::is_signed)>
constexpr To lossless_integral_conversion(const From from, int &ec) {
    ec = 0;
    using F = std::numeric_limits<From>;
    using T = std::numeric_limits<To>;
    static_assert(F::is_integer, "From must be integral");
    static_assert(T::is_integer, "To must be integral");

    if (F::is_signed && !T::is_signed) {
        // From may be negative, not allowed!
        if (abel::detail::is_negative(from)) {
            ec = 1;
            return {};
        }

        // From is positive. Can it always fit in To?
        if (F::digits <= T::digits) {
            // yes, From always fits in To.
        } else {
            // from may not fit in To, we have to do a dynamic check
            if (from > static_cast<From>((T::max)())) {
                ec = 1;
                return {};
            }
        }
    }

    if (!F::is_signed && T::is_signed) {
        // can from be held in To?
        if (F::digits < T::digits) {
            // yes, From always fits in To.
        } else {
            // from may not fit in To, we have to do a dynamic check
            if (from > static_cast<From>((T::max)())) {
                // outside range.
                ec = 1;
                return {};
            }
        }
    }

    // reaching here means all is ok for lossless conversion.
    return static_cast<To>(from);

}  // function

template<typename To, typename From,
        FMT_ENABLE_IF(std::is_same<From, To>::value)>
constexpr To lossless_integral_conversion(const From from, int &ec) {
    ec = 0;
    return from;
}  // function

// clang-format off
/**
 * converts From to To if possible, otherwise ec is set.
 *
 * input                            |    output
 * ---------------------------------|---------------
 * NaN                              | NaN
 * Inf                              | Inf
 * normal, fits in output           | converted (possibly lossy)
 * normal, does not fit in output   | ec is set
 * subnormal                        | best effort
 * -Inf                             | -Inf
 */
// clang-format on
template<typename To, typename From,
        FMT_ENABLE_IF(!std::is_same<From, To>::value)>
constexpr To safe_float_conversion(const From from, int &ec) {
    ec = 0;
    using T = std::numeric_limits<To>;
    static_assert(std::is_floating_point<From>::value, "From must be floating");
    static_assert(std::is_floating_point<To>::value, "To must be floating");

    // catch the only happy case
    if (std::isfinite(from)) {
        if (from >= T::lowest() && from <= (T::max)()) {
            return static_cast<To>(from);
        }
        // not within range.
        ec = 1;
        return {};
    }

    // nan and inf will be preserved
    return static_cast<To>(from);
}  // function

template<typename To, typename From,
        FMT_ENABLE_IF(std::is_same<From, To>::value)>
constexpr To safe_float_conversion(const From from, int &ec) {
    ec = 0;
    static_assert(std::is_floating_point<From>::value, "From must be floating");
    return from;
}

/**
 * safe duration cast between integral durations
 */
template<typename To, typename FromRep, typename FromPeriod,
        FMT_ENABLE_IF(std::is_integral<FromRep>::value),
        FMT_ENABLE_IF(std::is_integral<typename To::rep>::value)>
To safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
                      int &ec) {
    using From = std::chrono::duration<FromRep, FromPeriod>;
    ec = 0;
    // the basic idea is that we need to convert from count() in the from type
    // to count() in the To type, by multiplying it with this:
    struct Factor
            : std::ratio_divide<typename From::period, typename To::period> {
    };

    static_assert(Factor::num > 0, "num must be positive");
    static_assert(Factor::den > 0, "den must be positive");

    // the conversion is like this: multiply from.count() with Factor::num
    // /Factor::den and convert it to To::rep, all this without
    // overflow/underflow. let's start by finding a suitable type that can hold
    // both To, From and Factor::num
    using IntermediateRep =
    typename std::common_type<typename From::rep, typename To::rep,
            decltype(Factor::num)>::type;

    // safe conversion to IntermediateRep
    IntermediateRep count =
            lossless_integral_conversion<IntermediateRep>(from.count(), ec);
    if (ec) {
        return {};
    }
    // multiply with Factor::num without overflow or underflow
    if (Factor::num != 1) {
        const auto max1 = detail::max_value<IntermediateRep>() / Factor::num;
        if (count > max1) {
            ec = 1;
            return {};
        }
        const auto min1 =
                (std::numeric_limits<IntermediateRep>::min)() / Factor::num;
        if (count < min1) {
            ec = 1;
            return {};
        }
        count *= Factor::num;
    }

    // this can't go wrong, right? den>0 is checked earlier.
    if (Factor::den != 1) {
        count /= Factor::den;
    }
    // convert to the to type, safely
    using ToRep = typename To::rep;
    const ToRep tocount = lossless_integral_conversion<ToRep>(count, ec);
    if (ec) {
        return {};
    }
    return To{tocount};
}

/**
 * safe duration_cast between floating point durations
 */
template<typename To, typename FromRep, typename FromPeriod,
        FMT_ENABLE_IF(std::is_floating_point<FromRep>::value),
        FMT_ENABLE_IF(std::is_floating_point<typename To::rep>::value)>
To safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from,
                      int &ec) {
    using From = std::chrono::duration<FromRep, FromPeriod>;
    ec = 0;
    if (std::isnan(from.count())) {
        // nan in, gives nan out. easy.
        return To{std::numeric_limits<typename To::rep>::quiet_NaN()};
    }
    // maybe we should also check if from is denormal, and decide what to do about
    // it.

    // +-inf should be preserved.
    if (std::isinf(from.count())) {
        return To{from.count()};
    }

    // the basic idea is that we need to convert from count() in the from type
    // to count() in the To type, by multiplying it with this:
    struct Factor
            : std::ratio_divide<typename From::period, typename To::period> {
    };

    static_assert(Factor::num > 0, "num must be positive");
    static_assert(Factor::den > 0, "den must be positive");

    // the conversion is like this: multiply from.count() with Factor::num
    // /Factor::den and convert it to To::rep, all this without
    // overflow/underflow. let's start by finding a suitable type that can hold
    // both To, From and Factor::num
    using IntermediateRep =
    typename std::common_type<typename From::rep, typename To::rep,
            decltype(Factor::num)>::type;

    // force conversion of From::rep -> IntermediateRep to be safe,
    // even if it will never happen be narrowing in this context.
    IntermediateRep count =
            safe_float_conversion<IntermediateRep>(from.count(), ec);
    if (ec) {
        return {};
    }

    // multiply with Factor::num without overflow or underflow
    if (Factor::num != 1) {
        constexpr auto max1 = detail::max_value<IntermediateRep>() /
                              static_cast<IntermediateRep>(Factor::num);
        if (count > max1) {
            ec = 1;
            return {};
        }
        constexpr auto min1 = std::numeric_limits<IntermediateRep>::lowest() /
                              static_cast<IntermediateRep>(Factor::num);
        if (count < min1) {
            ec = 1;
            return {};
        }
        count *= static_cast<IntermediateRep>(Factor::num);
    }

    // this can't go wrong, right? den>0 is checked earlier.
    if (Factor::den != 1) {
        using common_t = typename std::common_type<IntermediateRep, intmax_t>::type;
        count /= static_cast<common_t>(Factor::den);
    }

    // convert to the to type, safely
    using ToRep = typename To::rep;

    const ToRep tocount = safe_float_conversion<ToRep>(count, ec);
    if (ec) {
        return {};
    }
    return To{tocount};
}
}  // namespace safe_duration_cast
#endif

// Prevents expansion of a preceding token as a function-style macro.
// Usage: f FMT_NOMACRO()
#define FMT_NOMACRO

namespace detail {
inline null<> localtime_r FMT_NOMACRO(...) { return null<>(); }

inline null<> localtime_s(...) { return null<>(); }

inline null<> gmtime_r(...) { return null<>(); }

inline null<> gmtime_s(...) { return null<>(); }
}  // namespace detail

// Thread-safe replacement for std::localtime
inline std::tm localtime(std::time_t time) {
    struct dispatcher {
        std::time_t time_;
        std::tm tm_;

        dispatcher(std::time_t t) : time_(t) {}

        bool run() {
            using namespace abel::detail;
            return handle(localtime_r(&time_, &tm_));
        }

        bool handle(std::tm *tm) { return tm != nullptr; }

        bool handle(detail::null<>) {
            using namespace abel::detail;
            return fallback(localtime_s(&tm_, &time_));
        }

        bool fallback(int res) { return res == 0; }

#if !defined(ABEL_COMPILER_MSVC)

        bool fallback(detail::null<>) {
            using namespace abel::detail;
            std::tm *tm = std::localtime(&time_);
            if (tm) tm_ = *tm;
            return tm != nullptr;
        }

#endif
    };
    dispatcher lt(time);
    // Too big time values may be unsupported.
    if (!lt.run()) ABEL_THROW(format_error("time_t value out of range"));
    return lt.tm_;
}

// Thread-safe replacement for std::gmtime
inline std::tm gmtime(std::time_t time) {
    struct dispatcher {
        std::time_t time_;
        std::tm tm_;

        dispatcher(std::time_t t) : time_(t) {}

        bool run() {
            using namespace abel::detail;
            return handle(gmtime_r(&time_, &tm_));
        }

        bool handle(std::tm *tm) { return tm != nullptr; }

        bool handle(detail::null<>) {
            using namespace abel::detail;
            return fallback(gmtime_s(&tm_, &time_));
        }

        bool fallback(int res) { return res == 0; }

#if !defined(ABEL_COMPILER_MSVC)

        bool fallback(detail::null<>) {
            std::tm *tm = std::gmtime(&time_);
            if (tm) tm_ = *tm;
            return tm != nullptr;
        }

#endif
    };
    dispatcher gt(time);
    // Too big time values may be unsupported.
    if (!gt.run()) ABEL_THROW(format_error("time_t value out of range"));
    return gt.tm_;
}

namespace detail {
inline size_t strftime(char *str, size_t count, const char *format,
                       const std::tm *time) {
    return std::strftime(str, count, format, time);
}

inline size_t strftime(wchar_t *str, size_t count, const wchar_t *format,
                       const std::tm *time) {
    return std::wcsftime(str, count, format, time);
}
}  // namespace detail

template<typename Char>
struct formatter<std::tm, Char> {
    template<typename ParseContext>
    auto parse(ParseContext &ctx) -> decltype(ctx.begin()) {
        auto it = ctx.begin();
        if (it != ctx.end() && *it == ':') ++it;
        auto end = it;
        while (end != ctx.end() && *end != '}') ++end;
        tm_format.reserve(detail::to_unsigned(end - it + 1));
        tm_format.append(it, end);
        tm_format.push_back('\0');
        return end;
    }

    template<typename FormatContext>
    auto format(const std::tm &tm, FormatContext &ctx) -> decltype(ctx.out()) {
        basic_memory_buffer<Char> buf;
        size_t start = buf.size();
        for (;;) {
            size_t size = buf.capacity() - start;
            size_t count = detail::strftime(&buf[start], size, &tm_format[0], &tm);
            if (count != 0) {
                buf.resize(start + count);
                break;
            }
            if (size >= tm_format.size() * 256) {
                // If the buffer is 256 times larger than the format string, assume
                // that `strftime` gives an empty result. There doesn't seem to be a
                // better way to distinguish the two cases:
                // https://github.com/fmtlib/fmt/issues/367
                break;
            }
            const size_t MIN_GROWTH = 10;
            buf.reserve(buf.capacity() + (size > MIN_GROWTH ? size : MIN_GROWTH));
        }
        return std::copy(buf.begin(), buf.end(), ctx.out());
    }

    basic_memory_buffer<Char> tm_format;
};

namespace detail {
template<typename Period>
constexpr const char *get_units() {
    return nullptr;
}

template<>
constexpr const char *get_units<std::atto>() { return "as"; }

template<>
constexpr const char *get_units<std::femto>() { return "fs"; }

template<>
constexpr const char *get_units<std::pico>() { return "ps"; }

template<>
constexpr const char *get_units<std::nano>() { return "ns"; }

template<>
constexpr const char *get_units<std::micro>() { return "µs"; }

template<>
constexpr const char *get_units<std::milli>() { return "ms"; }

template<>
constexpr const char *get_units<std::centi>() { return "cs"; }

template<>
constexpr const char *get_units<std::deci>() { return "ds"; }

template<>
constexpr const char *get_units<std::ratio<1>>() { return "s"; }

template<>
constexpr const char *get_units<std::deca>() { return "das"; }

template<>
constexpr const char *get_units<std::hecto>() { return "hs"; }

template<>
constexpr const char *get_units<std::kilo>() { return "ks"; }

template<>
constexpr const char *get_units<std::mega>() { return "Ms"; }

template<>
constexpr const char *get_units<std::giga>() { return "Gs"; }

template<>
constexpr const char *get_units<std::tera>() { return "Ts"; }

template<>
constexpr const char *get_units<std::peta>() { return "Ps"; }

template<>
constexpr const char *get_units<std::exa>() { return "Es"; }

template<>
constexpr const char *get_units<std::ratio<60>>() {
    return "m";
}

template<>
constexpr const char *get_units<std::ratio<3600>>() {
    return "h";
}

enum class numeric_system {
    standard,
    // Alternative numeric system, e.g. 十二 instead of 12 in ja_JP locale.
    alternative
};

// Parses a put_time-like format string and invokes handler actions.
template<typename Char, typename Handler>
constexpr const Char *parse_chrono_format(const Char *begin,
                                          const Char *end,
                                          Handler &&handler) {
    auto ptr = begin;
    while (ptr != end) {
        auto c = *ptr;
        if (c == '}') break;
        if (c != '%') {
            ++ptr;
            continue;
        }
        if (begin != ptr) handler.on_text(begin, ptr);
        ++ptr;  // consume '%'
        if (ptr == end) ABEL_THROW(format_error("invalid format"));
        c = *ptr++;
        switch (c) {
            case '%':
                handler.on_text(ptr - 1, ptr);
                break;
            case 'n': {
                const Char newline[] = {'\n'};
                handler.on_text(newline, newline + 1);
                break;
            }
            case 't': {
                const Char tab[] = {'\t'};
                handler.on_text(tab, tab + 1);
                break;
            }
                // Day of the week:
            case 'a':
                handler.on_abbr_weekday();
                break;
            case 'A':
                handler.on_full_weekday();
                break;
            case 'w':
                handler.on_dec0_weekday(numeric_system::standard);
                break;
            case 'u':
                handler.on_dec1_weekday(numeric_system::standard);
                break;
                // Month:
            case 'b':
                handler.on_abbr_month();
                break;
            case 'B':
                handler.on_full_month();
                break;
                // Hour, minute, second:
            case 'H':
                handler.on_24_hour(numeric_system::standard);
                break;
            case 'I':
                handler.on_12_hour(numeric_system::standard);
                break;
            case 'M':
                handler.on_minute(numeric_system::standard);
                break;
            case 'S':
                handler.on_second(numeric_system::standard);
                break;
                // Other:
            case 'c':
                handler.on_datetime(numeric_system::standard);
                break;
            case 'x':
                handler.on_loc_date(numeric_system::standard);
                break;
            case 'X':
                handler.on_loc_time(numeric_system::standard);
                break;
            case 'D':
                handler.on_us_date();
                break;
            case 'F':
                handler.on_iso_date();
                break;
            case 'r':
                handler.on_12_hour_time();
                break;
            case 'R':
                handler.on_24_hour_time();
                break;
            case 'T':
                handler.on_iso_time();
                break;
            case 'p':
                handler.on_am_pm();
                break;
            case 'Q':
                handler.on_duration_value();
                break;
            case 'q':
                handler.on_duration_unit();
                break;
            case 'z':
                handler.on_utc_offset();
                break;
            case 'Z':
                handler.on_tz_name();
                break;
                // Alternative representation:
            case 'E': {
                if (ptr == end) ABEL_THROW(format_error("invalid format"));
                c = *ptr++;
                switch (c) {
                    case 'c':
                        handler.on_datetime(numeric_system::alternative);
                        break;
                    case 'x':
                        handler.on_loc_date(numeric_system::alternative);
                        break;
                    case 'X':
                        handler.on_loc_time(numeric_system::alternative);
                        break;
                    default:
                        ABEL_THROW(format_error("invalid format"));
                }
                break;
            }
            case 'O':
                if (ptr == end) ABEL_THROW(format_error("invalid format"));
                c = *ptr++;
                switch (c) {
                    case 'w':
                        handler.on_dec0_weekday(numeric_system::alternative);
                        break;
                    case 'u':
                        handler.on_dec1_weekday(numeric_system::alternative);
                        break;
                    case 'H':
                        handler.on_24_hour(numeric_system::alternative);
                        break;
                    case 'I':
                        handler.on_12_hour(numeric_system::alternative);
                        break;
                    case 'M':
                        handler.on_minute(numeric_system::alternative);
                        break;
                    case 'S':
                        handler.on_second(numeric_system::alternative);
                        break;
                    default:
                        ABEL_THROW(format_error("invalid format"));
                }
                break;
            default:
                ABEL_THROW(format_error("invalid format"));
        }
        begin = ptr;
    }
    if (begin != ptr) handler.on_text(begin, ptr);
    return ptr;
}

struct chrono_format_checker {
    ABEL_NORETURN void report_no_date() { ABEL_THROW(format_error("no date")); }

    template<typename Char>
    void on_text(const Char *, const Char *) {}

    ABEL_NORETURN void on_abbr_weekday() { report_no_date(); }

    ABEL_NORETURN void on_full_weekday() { report_no_date(); }

    ABEL_NORETURN void on_dec0_weekday(numeric_system) { report_no_date(); }

    ABEL_NORETURN void on_dec1_weekday(numeric_system) { report_no_date(); }

    ABEL_NORETURN void on_abbr_month() { report_no_date(); }

    ABEL_NORETURN void on_full_month() { report_no_date(); }

    void on_24_hour(numeric_system) {}

    void on_12_hour(numeric_system) {}

    void on_minute(numeric_system) {}

    void on_second(numeric_system) {}

    ABEL_NORETURN void on_datetime(numeric_system) { report_no_date(); }

    ABEL_NORETURN void on_loc_date(numeric_system) { report_no_date(); }

    ABEL_NORETURN void on_loc_time(numeric_system) { report_no_date(); }

    ABEL_NORETURN void on_us_date() { report_no_date(); }

    ABEL_NORETURN void on_iso_date() { report_no_date(); }

    void on_12_hour_time() {}

    void on_24_hour_time() {}

    void on_iso_time() {}

    void on_am_pm() {}

    void on_duration_value() {}

    void on_duration_unit() {}

    ABEL_NORETURN void on_utc_offset() { report_no_date(); }

    ABEL_NORETURN void on_tz_name() { report_no_date(); }
};

template<typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
inline bool isnan(T) {
    return false;
}

template<typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value)>
inline bool isnan(T value) {
    return std::isnan(value);
}

template<typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
inline bool isfinite(T) {
    return true;
}

template<typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value)>
inline bool isfinite(T value) {
    return std::isfinite(value);
}

// Converts value to int and checks that it's in the range [0, upper).
template<typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
inline int to_nonnegative_int(T value, int upper) {
    ABEL_ASSERT_MSG(value >= 0 && value <= upper, "invalid value");
    (void) upper;
    return static_cast<int>(value);
}

template<typename T, FMT_ENABLE_IF(!std::is_integral<T>::value)>
inline int to_nonnegative_int(T value, int upper) {
    ABEL_ASSERT_MSG(
            std::isnan(value) || (value >= 0 && value <= static_cast<T>(upper)),
            "invalid value");
    (void) upper;
    return static_cast<int>(value);
}

template<typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
inline T mod(T x, int y) {
    return x % static_cast<T>(y);
}

template<typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value)>
inline T mod(T x, int y) {
    return std::fmod(x, static_cast<T>(y));
}

// If T is an integral type, maps T to its unsigned counterpart, otherwise
// leaves it unchanged (unlike std::make_unsigned).
template<typename T, bool INTEGRAL = std::is_integral<T>::value>
struct make_unsigned_or_unchanged {
    using type = T;
};

template<typename T>
struct make_unsigned_or_unchanged<T, true> {
    using type = typename std::make_unsigned<T>::type;
};

#if FMT_SAFE_DURATION_CAST

// throwing version of safe_duration_cast
template<typename To, typename FromRep, typename FromPeriod>
To fmt_safe_duration_cast(std::chrono::duration<FromRep, FromPeriod> from) {
    int ec;
    To to = safe_duration_cast::safe_duration_cast<To>(from, ec);
    if (ec) ABEL_THROW(format_error("cannot format duration"));
    return to;
}

#endif

template<typename Rep, typename Period,
        FMT_ENABLE_IF(std::is_integral<Rep>::value)>
inline std::chrono::duration<Rep, std::milli> get_milliseconds(
        std::chrono::duration<Rep, Period> d) {
    // this may overflow and/or the result may not fit in the
    // target type.
#if FMT_SAFE_DURATION_CAST
    using CommonSecondsType =
    typename std::common_type<decltype(d), std::chrono::seconds>::type;
    const auto d_as_common = fmt_safe_duration_cast<CommonSecondsType>(d);
    const auto d_as_whole_seconds =
            fmt_safe_duration_cast<std::chrono::seconds>(d_as_common);
    // this conversion should be nonproblematic
    const auto diff = d_as_common - d_as_whole_seconds;
    const auto ms =
            fmt_safe_duration_cast<std::chrono::duration<Rep, std::milli>>(diff);
    return ms;
#else
    auto s = std::chrono::duration_cast<std::chrono::seconds>(d);
    return std::chrono::duration_cast<std::chrono::milliseconds>(d - s);
#endif
}

template<typename Rep, typename Period,
        FMT_ENABLE_IF(std::is_floating_point<Rep>::value)>
inline std::chrono::duration<Rep, std::milli> get_milliseconds(
        std::chrono::duration<Rep, Period> d) {
    using common_type = typename std::common_type<Rep, std::intmax_t>::type;
    auto ms = mod(d.count() * static_cast<common_type>(Period::num) /
                  static_cast<common_type>(Period::den) * 1000,
                  1000);
    return std::chrono::duration<Rep, std::milli>(static_cast<Rep>(ms));
}

template<typename Char, typename Rep, typename OutputIt>
OutputIt format_duration_value(OutputIt out, Rep val, int precision) {
    const Char pr_f[] = {'{', ':', '.', '{', '}', 'f', '}', 0};
    if (precision >= 0) return format_to(out, pr_f, val, precision);
    const Char fp_f[] = {'{', ':', 'g', '}', 0};
    const Char format[] = {'{', '}', 0};
    return format_to(out, std::is_floating_point<Rep>::value ? fp_f : format,
                     val);
}

template<typename Char, typename OutputIt>
OutputIt copy_unit(string_view unit, OutputIt out, Char) {
    return std::copy(unit.begin(), unit.end(), out);
}

template<typename OutputIt>
OutputIt copy_unit(string_view unit, OutputIt out, wchar_t) {
    // This works when wchar_t is UTF-32 because units only contain characters
    // that have the same representation in UTF-16 and UTF-32.
    utf8_to_utf16 u(unit);
    return std::copy(u.c_str(), u.c_str() + u.size(), out);
}

template<typename Char, typename Period, typename OutputIt>
OutputIt format_duration_unit(OutputIt out) {
    if (const char *unit = get_units<Period>())
        return copy_unit(string_view(unit), out, Char());
    const Char num_f[] = {'[', '{', '}', ']', 's', 0};
    if (const_check(Period::den == 1)) return format_to(out, num_f, Period::num);
    const Char num_def_f[] = {'[', '{', '}', '/', '{', '}', ']', 's', 0};
    return format_to(out, num_def_f, Period::num, Period::den);
}

template<typename FormatContext, typename OutputIt, typename Rep,
        typename Period>
struct chrono_formatter {
    FormatContext &context;
    OutputIt out;
    int precision;
    // rep is unsigned to avoid overflow.
    using rep =
    conditional_t<std::is_integral<Rep>::value && sizeof(Rep) < sizeof(int),
            unsigned, typename make_unsigned_or_unchanged<Rep>::type>;
    rep val;
    using seconds = std::chrono::duration<rep>;
    seconds s;
    using milliseconds = std::chrono::duration<rep, std::milli>;
    bool negative;

    using char_type = typename FormatContext::char_type;

    explicit chrono_formatter(FormatContext &ctx, OutputIt o,
                              std::chrono::duration<Rep, Period> d)
            : context(ctx),
              out(o),
              val(static_cast<rep>(d.count())),
              negative(false) {
        if (d.count() < 0) {
            val = 0 - val;
            negative = true;
        }

        // this may overflow and/or the result may not fit in the
        // target type.
#if FMT_SAFE_DURATION_CAST
        // might need checked conversion (rep!=Rep)
        auto tmpval = std::chrono::duration<rep, Period>(val);
        s = fmt_safe_duration_cast<seconds>(tmpval);
#else
        s = std::chrono::duration_cast<seconds>(
            std::chrono::duration<rep, Period>(val));
#endif
    }

    // returns true if nan or inf, writes to out.
    bool handle_nan_inf() {
        if (isfinite(val)) {
            return false;
        }
        if (isnan(val)) {
            write_nan();
            return true;
        }
        // must be +-inf
        if (val > 0) {
            write_pinf();
        } else {
            write_ninf();
        }
        return true;
    }

    Rep hour() const { return static_cast<Rep>(mod((s.count() / 3600), 24)); }

    Rep hour12() const {
        Rep hour = static_cast<Rep>(mod((s.count() / 3600), 12));
        return hour <= 0 ? 12 : hour;
    }

    Rep minute() const { return static_cast<Rep>(mod((s.count() / 60), 60)); }

    Rep second() const { return static_cast<Rep>(mod(s.count(), 60)); }

    std::tm time() const {
        auto time = std::tm();
        time.tm_hour = to_nonnegative_int(hour(), 24);
        time.tm_min = to_nonnegative_int(minute(), 60);
        time.tm_sec = to_nonnegative_int(second(), 60);
        return time;
    }

    void write_sign() {
        if (negative) {
            *out++ = '-';
            negative = false;
        }
    }

    void write(Rep value, int width) {
        write_sign();
        if (isnan(value)) return write_nan();
        uint32_or_64_or_128_t<int> n =
                to_unsigned(to_nonnegative_int(value, max_value<int>()));
        int num_digits = detail::count_digits(n);
        if (width > num_digits) out = std::fill_n(out, width - num_digits, '0');
        out = format_decimal<char_type>(out, n, num_digits).end;
    }

    void write_nan() { std::copy_n("nan", 3, out); }

    void write_pinf() { std::copy_n("inf", 3, out); }

    void write_ninf() { std::copy_n("-inf", 4, out); }

    void format_localized(const tm &time, char format, char modifier = 0) {
        if (isnan(val)) return write_nan();
        auto locale = context.locale().template get<std::locale>();
        auto &facet = std::use_facet<std::time_put<char_type>>(locale);
        std::basic_ostringstream<char_type> os;
        os.imbue(locale);
        facet.put(os, os, ' ', &time, format, modifier);
        auto str = os.str();
        std::copy(str.begin(), str.end(), out);
    }

    void on_text(const char_type *begin, const char_type *end) {
        std::copy(begin, end, out);
    }

    // These are not implemented because durations don't have date information.
    void on_abbr_weekday() {}

    void on_full_weekday() {}

    void on_dec0_weekday(numeric_system) {}

    void on_dec1_weekday(numeric_system) {}

    void on_abbr_month() {}

    void on_full_month() {}

    void on_datetime(numeric_system) {}

    void on_loc_date(numeric_system) {}

    void on_loc_time(numeric_system) {}

    void on_us_date() {}

    void on_iso_date() {}

    void on_utc_offset() {}

    void on_tz_name() {}

    void on_24_hour(numeric_system ns) {
        if (handle_nan_inf()) return;

        if (ns == numeric_system::standard) return write(hour(), 2);
        auto time = tm();
        time.tm_hour = to_nonnegative_int(hour(), 24);
        format_localized(time, 'H', 'O');
    }

    void on_12_hour(numeric_system ns) {
        if (handle_nan_inf()) return;

        if (ns == numeric_system::standard) return write(hour12(), 2);
        auto time = tm();
        time.tm_hour = to_nonnegative_int(hour12(), 12);
        format_localized(time, 'I', 'O');
    }

    void on_minute(numeric_system ns) {
        if (handle_nan_inf()) return;

        if (ns == numeric_system::standard) return write(minute(), 2);
        auto time = tm();
        time.tm_min = to_nonnegative_int(minute(), 60);
        format_localized(time, 'M', 'O');
    }

    void on_second(numeric_system ns) {
        if (handle_nan_inf()) return;

        if (ns == numeric_system::standard) {
            write(second(), 2);
#if FMT_SAFE_DURATION_CAST
            // convert rep->Rep
            using duration_rep = std::chrono::duration<rep, Period>;
            using duration_Rep = std::chrono::duration<Rep, Period>;
            auto tmpval = fmt_safe_duration_cast<duration_Rep>(duration_rep{val});
#else
            auto tmpval = std::chrono::duration<Rep, Period>(val);
#endif
            auto ms = get_milliseconds(tmpval);
            if (ms != std::chrono::milliseconds(0)) {
                *out++ = '.';
                write(ms.count(), 3);
            }
            return;
        }
        auto time = tm();
        time.tm_sec = to_nonnegative_int(second(), 60);
        format_localized(time, 'S', 'O');
    }

    void on_12_hour_time() {
        if (handle_nan_inf()) return;
        format_localized(time(), 'r');
    }

    void on_24_hour_time() {
        if (handle_nan_inf()) {
            *out++ = ':';
            handle_nan_inf();
            return;
        }

        write(hour(), 2);
        *out++ = ':';
        write(minute(), 2);
    }

    void on_iso_time() {
        on_24_hour_time();
        *out++ = ':';
        if (handle_nan_inf()) return;
        write(second(), 2);
    }

    void on_am_pm() {
        if (handle_nan_inf()) return;
        format_localized(time(), 'p');
    }

    void on_duration_value() {
        if (handle_nan_inf()) return;
        write_sign();
        out = format_duration_value<char_type>(out, val, precision);
    }

    void on_duration_unit() {
        out = format_duration_unit<char_type, Period>(out);
    }
};
}  // namespace detail

template<typename Rep, typename Period, typename Char>
struct formatter<std::chrono::duration<Rep, Period>, Char> {
  private:
    basic_format_specs<Char> specs;
    int precision;
    using arg_ref_type = detail::arg_ref<Char>;
    arg_ref_type width_ref;
    arg_ref_type precision_ref;
    mutable basic_string_view<Char> format_str;
    using duration = std::chrono::duration<Rep, Period>;

    struct spec_handler {
        formatter &f;
        basic_format_parse_context<Char> &context;
        basic_string_view<Char> format_str;

        template<typename Id>
        constexpr arg_ref_type make_arg_ref(Id arg_id) {
            context.check_arg_id(arg_id);
            return arg_ref_type(arg_id);
        }

        constexpr arg_ref_type make_arg_ref(basic_string_view<Char> arg_id) {
            context.check_arg_id(arg_id);
            return arg_ref_type(arg_id);
        }

        constexpr arg_ref_type make_arg_ref(detail::auto_id) {
            return arg_ref_type(context.next_arg_id());
        }

        void on_error(const char *msg) { ABEL_THROW(format_error(msg)); }

        void on_fill(basic_string_view<Char> fill) { f.specs.fill = fill; }

        void on_align(align_t align) { f.specs.align = align; }

        void on_width(int width) { f.specs.width = width; }

        void on_precision(int _precision) { f.precision = _precision; }

        void end_precision() {}

        template<typename Id>
        void on_dynamic_width(Id arg_id) {
            f.width_ref = make_arg_ref(arg_id);
        }

        template<typename Id>
        void on_dynamic_precision(Id arg_id) {
            f.precision_ref = make_arg_ref(arg_id);
        }
    };

    using iterator = typename basic_format_parse_context<Char>::iterator;
    struct parse_range {
        iterator begin;
        iterator end;
    };

    constexpr parse_range do_parse(basic_format_parse_context<Char> &ctx) {
        auto begin = ctx.begin(), end = ctx.end();
        if (begin == end || *begin == '}') return {begin, begin};
        spec_handler handler{*this, ctx, format_str};
        begin = detail::parse_align(begin, end, handler);
        if (begin == end) return {begin, begin};
        begin = detail::parse_width(begin, end, handler);
        if (begin == end) return {begin, begin};
        if (*begin == '.') {
            if (std::is_floating_point<Rep>::value)
                begin = detail::parse_precision(begin, end, handler);
            else
                handler.on_error("precision not allowed for this argument type");
        }
        end = parse_chrono_format(begin, end, detail::chrono_format_checker());
        return {begin, end};
    }

  public:
    formatter() : precision(-1) {}

    constexpr auto parse(basic_format_parse_context<Char> &ctx)
    -> decltype(ctx.begin()) {
        auto range = do_parse(ctx);
        format_str = basic_string_view<Char>(
                &*range.begin, detail::to_unsigned(range.end - range.begin));
        return range.end;
    }

    template<typename FormatContext>
    auto format(const duration &d, FormatContext &ctx) -> decltype(ctx.out()) {
        auto begin = format_str.begin(), end = format_str.end();
        // As a possible future optimization, we could avoid extra copying if width
        // is not specified.
        basic_memory_buffer<Char> buf;
        auto out = std::back_inserter(buf);
        detail::handle_dynamic_spec<detail::width_checker>(specs.width, width_ref,
                                                           ctx);
        detail::handle_dynamic_spec<detail::precision_checker>(precision,
                                                               precision_ref, ctx);
        if (begin == end || *begin == '}') {
            out = detail::format_duration_value<Char>(out, d.count(), precision);
            detail::format_duration_unit<Char, Period>(out);
        } else {
            detail::chrono_formatter<FormatContext, decltype(out), Rep, Period> f(
                    ctx, out, d);
            f.precision = precision;
            parse_chrono_format(begin, end, f);
        }
        return detail::write(
                ctx.out(), basic_string_view<Char>(buf.data(), buf.size()), specs);
    }
};

FMT_END_NAMESPACE

#endif  // ABEL_STRINGS_INTERNAL_CHRONO_H_
